This invention relates to a combined electrographic printing, copying, and telefax machine. More specifically, the present invention relates to a compact electrographic printing apparatus which is capable of:
(1) scanning and copying an original document,
(2) receiving and printing information derived from a local source, such as information derived from a computer connected to the apparatus,
(3) receiving and printing information derived from a remote source, for example, information derived from a remote computer or telefax machine, and
(4) scanning an original document and transmitting the information thereon to a remote source via the telephone lines.
All of the foregoing printing functions are performed on plain paper using an electrographic or xerographic printing engine which, in one particularly preferred embodiment, includes horizontally disposed photoconductive belt.
In the process of electrographic or xerographic printing, a photoconductive member is employed to record an image on a photosensitive surface. The photoconductive member, which may typically take the form of a belt or a drum, is charged to a substantially uniform potential to sensitize its surface. A light is then employed to discharge selected areas of the photosensitive surface to form an electrostatic latent image on the photoconductive member.
In the case of a copying machine, an original document is exposed to high intensity light. Through the use of a slit aperture, mirrors, and various other optical components, the reflected light image of the original document is shined onto a sensitized photoconductive member where it discharges selected areas of the photosensitive surface. This light image is recorded as an electrostatic latent image on the photoconductive member and it corresponds to the informational areas contained on the original document.
In the case of an electrographic printer connected to a computer, a similar process is used to record information on the photoconductive member. The charged portion of the photosensitive surface is exposed to a light image, the shape of which is controlled by input signals from the computer. For example, a laser or an LED array functions as an optical print head and illuminates the photoconductive member with a light image, the characteristic shape of which is controlled by a stream of data from the computer. Here too, an electrostatic latent image corresponding to desired informational area is recorded on the photoconductive member.
After recording the electrostatic latent image on the photoconductive member, the latent image is developed by bringing a developer material or toner into contact with it. The developer material comprises triboelectrically charged toner particles which are attracted to the electrostatic latent image. The toner particles form a mirror image on the photoconductive member corresponding to the electrostatic latent image. This powder image is subsequently transferred to a sheet of recording medium, such as a sheet of paper, by a transfer unit. In general, the transfer unit comprises a corona charger which creates a high intensity electric field of suitable polarity about the sheet of paper. The powder image, comprising charged toner particles on the photoconductive member are attracted and transferred to the sheet. Thereafter, the powder image is permanently affixed to the sheet in image configuration by a variety of methods such as by fusing, and the sheet is ejected.
The above-mentioned operations may be carried out by arranging a number of stations in sequence about the photoconductive member. Thus, the photoconductive member is usually surrounded in sequence by a charging station to charge the photoconductive member, an imaging station to form an electrostatic latent image on the photoconductive member, a developing station to develop the electrostatic latent image on the photoconductive member, and a transfer station to transfer the developed image from the photoconductive member to the sheet of recording medium. A discharging station and a cleaning station are also arranged about the photoconductive member to ready it for use again.
The assignee of the present invention has disclosed an claimed a high speed electrographic printer/copier and components thereof in a number of patent applications. A basic objective of the assignee has been to design the electrographic printer/copier from modular components. These modular components can be easily replaced when their useful lives have been exceeded or when they become defective. The electrographic printer/copier is described in application Ser. No. 700,813, filed Feb. 11, 1985, now U.S. Pat. No. 4,664,507. A photoconductive belt in the form of a disposable cassette with a charging unit attached thereto is described in application Ser. No. 718,947, filed Apr. 2, 1985, now U.S. Pat. No. 4,657,369. A developer unit containing a disposable toner cartridge is described in application Ser. No. 718,946, filed Apr. 2, 1985, now U.S. Pat. No. 4,639,116. A paper input cassette is disclosed in application Ser. No. 718,945, filed Apr. 2, 1985. Two different modular cleaning units for attachment to the photoconductive belt are described in application Ser. No. 033,458, filed Apr. 1, 1987, and application Ser. No. 033,457, filed Apr. 1, 1987. All of the above applications and patents have been assigned to the present assignee and all are incorporated herein by reference.
Telefax transmitting and receiving machines, also known as facsimile machines, resemble electrographic copiers and printers in many respects. Typically, telefax machines include a device for scanning an original document and for digitizing the scanned image, and a printing engine. Advanced high speed, high resolution, telefax machines employ charge-coupled devices (CCD's) for digitizing the scanned image. All CCD's are basically shift registers which digitize analog information and store the digitized information until it is delivered as an electrical signal. CCD's have been utilized as image sending devices for a variety of purposes. In particular, CCD linear arrays have been used as linear sensing devices in high performance telefax machines. To transmit information, such as graphics or text, on a sheet of paper via a telefax machine, the sheet of paper is scanned with a high intensity light and the image is focused onto a CCD linear array. The CCD digitizes the image and converts it into a stream of data, or bit stream. This bit stream, which optionally may be compressed by a variety of known techniques, is then transmitted over the telephone lines to a remote location using a modem.
A telefax machine or a computer at the remote location includes a modem to receive the bit stream over the telephone lines. After decompression when required, the bit stream controls the operation of a print engine to reproduce the information contained on the scanned original document. Telefax machines are known which employ an electrographic process to reproduce the original document at a remote location. Thus, in a process very similar to that described above for a printer, the bit stream received at the remote location can control an optical print head to focus an image on a photoconductive member and thereby produce a electrostatic latent image thereon corresponding to the original document. The electrostatic latent image can then be developed with a toner to form a powder image which is then transferred and fused to a sheet of plain paper.
As copiers, printers and telefax machines can all be adapted to employ an electrographic process to print information on a sheet of recording medium, it would be desirable to provide a single machine which is switchable between copying, printing, and telefax transmitting and receiving modes.
It is therefore an object of the present invention to provide a machine which is capable of scanning an original document, reproducing the scanned image on a sheet of paper, digitizing and sending the scanned image to a remote location, and printing digitized information received from a local or a remote source.
It is a further object of the present invention to provide such a machine which employs an electrographic print engine to carry out its printing functions.
It is a further object of the present invention to provide such a machine which utilizes many of the modular components of applicant's previously disclosed and claimed electrographic printer/copier.
It is a further object of the present invention to provide such an electrographic printing apparatus which is compact and has a low profile.
It is yet another object of the present invention to provide such an electrographic printing apparatus which has a simple paper path.
It is yet another object of the present invention to provide such an electrographic printing apparatus which employs a biased transfer roller to transfer a developed latent image to a sheet of the recording medium.
As used herein, the term "electrographic printing apparatus" and the like are intended to include copiers, printers and telefax machines which employ a photoconductive member to print information on a sheet of recording medium.